1. Field of the Invention
The present invention relates generally to precision optical inspection apparatus and, more particularly to apparatus for performing microscopic inspection and measuring of workpieces, such as integrated circuits and the like. The invention has particular application to microscopes used in combination with electronic image processing devices, such as video cameras and monitors.
2. Description of the Prior Art
Variable magnification microscopes, of the type used in the fabrication of integrated circuit semiconductor devices and the like, typically include turret-mounted multiple objective lenses. Such a standard multiple-objective microscope is disadvantageous because the objective turret and its associated lenses occupy considerable space, which is at a premium in work on microelectronic circuits. This is because a large amount of peripheral equipment, including probes, environmental chambers and the like, must commonly be disposed in close proximity with the workpiece. This equipment is typically fitted around the various objective lenses. Therefore, whenever it is necessary to switch to a different magnification objective, it is necessary to move some or all of the peripheral equipment and/or to back off the microscope to clear the equipment, so that there is room to swing the desired objective into position.
In many cases frequent objective changing is necessary in order to simply allow the operator to keep track of the specific location on the overall workpiece where the work is being performed. Thus, initially the operator may have to use an objective giving a wide field of view in order to locate a particular region on the workpiece to be viewed and then would switch to a higher magnification to give a narrow field of view of the specific region of interest. Typically, each time the operator wishes to move the field of view to a different region of interest it may be necessary to switch back to a wide field of view objective to locate the next region. If the objective is sealed in an environmental chamber, it is necessary to unseal it and to reseal the new objective in the chamber and permit time for the new objective to acclimate to the environment.
It is known to provide a microscope with a single replaceable objective lens. While this does not occupy as much space as a turret-mounted array of objective lenses, typically the mounting and demounting of the objective lens in order to effect replacement is complicated and time consuming.
Frequently, lasers are used in the processing of microelectronic circuits for removing passivation, cutting lines and holes, and the like, as well as for failure analysis. Typically, the laser beam is passed through all of the optics of the microscope, which entails significant loss. Thus, only a small percentage of the laser light from the source may reach the workpiece.